Tips on AVNRT ablation

Tips on AVNRT ablation

Anterior inputs to the AV node: fast pathway – seldom done now
Posterior inputs to AV node: Slow pathway – the main target for ablation in AVNRT
Area of interest for atrioventricular nodal re-entrant tachycardia (AVNRT) ablation: Triangle of Koch bounded by Coronary sinus (CS) os, septal tricuspid leaflet (STL) and Tendon of Todaro; His Bundle is at the apex of the triangle. If the Koch’s triangle is small, there is a higher risk of complete heart block (CHB) – More likely in children;
In elderly the CS os is higher and the triangle becomes smaller and and there is a higher chance of CHB

Left anterior oblique (LAO) view is foreshortened while RAO view can pick up supero-inferior catheter tip movements better during slow pathway ablation. Slow pathway ablation is done near the superior lip of the coronary sinus.

Successful ablation AVNRT site: accelerated junctional rhythm is seen. Stop the ablation even when there is VA block in a single beat. End point for slow pathway ablation: Complete elimination of slow pathway conduction or a single echo beat during isoprenaline stimulation is indicative of successful ablation.

Ideally, only those who need catecholamines for induction of tachycardia prior to ablation need re-stimulation after ablation to check for efficacy of ablation. However, if isoprenaline stimulation is used for documentation of success, the recurrence rate will be lower.

AVNRT ablation in elderly: Elderly are often more symptomatic, triangle of Koch is more horizontal, associated structural heart disease is more common.

AVNRT ablation in children: AV block incidence is slightly more, long term follow up has shown it to be a safe procedure. Cryoablation is being used more often in children and is replacing RFA.

Gradual power titration can reduce incidence of CHB. Linear posterior lesion from CS to tricuspid annulus is safe. Cryo ablation has lower rates of CHB and there is no epicardial coronary injury with cryo. Fluro time is also reduced with cryo as the catheter adheres (cryoadherence) to the site and repeat fluro is not needed during the ablation period.

Non contact mapping in AVNRT ablation is reserved for refractory cases. Magnetic navigation systems are also being used now a days, but are not too relevant for AVNRT ablation.

Ablation at the floor of the CS can cause inappropriate sinus tachycardia due to injury to the ganglia. Vagal stimulation during ablation in floor of the CS can cause AV block with simultaneous sinus bradycardia. This will not be an indication for stopping ablation. A shot of atropine can be given and we can continue with ablation.

A large CS may make the ablation site more closer to the compact AV node if we take a CS catheter going along the roof of the CS as a guide. CS angio can be used to delineate the CS size in this case. CS floor can be delineated by a catheter introduced from above through the internal jugular vein.
During slow pathway ablation, RAO view is used to ensure that the catheter is on the septum, which is identified by the up and down movement of the tip. If it is away from the septum the tip will move side to side in this view.

Fast pathway ablation is done in fast – fast pathway AVNRT, a very rare form of AVNRT. Fast pathway ablation has also been done when an IVC stent prevents ablation of slow pathway.

Left sided extension of slow pathway can occur in atypical AVNRT, requiring ablation deeper in the CS or in the middle cardiac vein. This breaks the rule that CS ablation should be done nearer the CS ostium to prevent coronary injury.

Junctional acceleration during ablation may not be seen when the sinus rate is high.

End point for ablation should be stricter for slow pathway ablation in atypical AVNRT. Otherwise the recurrence rate is high.